Various energy saving devices, developed according to the principles of fluid and ship dynamics and mounted at the stern of a ship, are currently known. One such device improves a ship's impelling force by making use of the rotational flow energy provided by a ship's propeller. A guiding wheel is coaxially mounted behind a ship's propeller. This guiding wheel has blades arranged in an outer circle and an inner circle. The blades of the inner circle are a set of hydraulic turbine blades which are located just within the range of the rotational energy of the propeller. The blades of the outer circle are propeller blades beyond the range of the rotational energy of the propeller. When the propeller of the ship rotates, the rotational flow energy produced by the propeller impacts on the hydraulic turbine blades of the inner circle, making the whole guiding wheel rotate at a low speed. At the same time, the propeller blades of the outer circle rotate and produce an additional impelling force which results in an increase in the speed of the ship.
Another type of energy saving device mounted at the stern is a compensating guide pipe. The pipe device guides the incoming flow for the ship's propeller. The guide pipe consists of two right and left half rings with the longitudinal profile of an aerofoil. The guide pipe is mounted in front of a stern-mounted propeller and slightly above the propeller. When the fast water mass points coming out of the half rings pass through the upper portion of the propeller, they accelerate the low speed incoming flow already there. Meanwhile, the low speed water mass points passing the outer surface of the half rings will decelerate the high speed incoming flow at a distance from the surface of a ship body. This improves the inhomogeneity of the incoming flow states of the propeller and the impelling efficiency of the ship.
A bow-mounted energy saving device is also known. It is a bulb-nosed structure which aims at decreasing the curvature change of a ship's bow. This device is designed to lower the viscous pressure resistance. At the same time, this device produces waves which have phase opposite and amplitude equal to the waves at the bow of the ship. The superposition of these device-produced waves results in the decrease or elimination of the resistance of making waves at the outside of the bow. This improves the ship's speed. However, this kind of bulb-nosed structure has only a limited energy saving effect, since the effect of decreasing the resistance and energy consumption depends upon the design of the curvature change of the spherical body of the device. Also, the formation of a spherical body at the bow creates difficulties in ship building.
Known devices, used individually or in combination, lower the total water resistance against a ship by about 18%. The present invention lowers the total water resistance against a ship by approximately 30%.